Set by Dr Eric Boa
The theme this month is “forgotten or overlooked plant parts’. The most revealing changes and alterations in growth, in relation to biotic and abiotic influences, often occur within stems, trunks and roots. It takes a little effort to look inside an unhealthy plant, yet it’s easy to concentrate on above ground plant parts. I am as guilty of this as others. but there’s almost always a hidden reward: the rotten root with mycelial growth, a stem with clearly demarcated staining, roots with strange growths – and so on. Carry a knife, is my advice, and a small digging tool, too, if you can. In the meanwhile, welcome to the
#1. Soyabean growth was uneven, yet there were no obvious disease symptoms. These growths were found on the roots. What are they?
The correct answer is:
Nitrogen-fixing nodules. Note their uniformity.
Comments:
Nematode galls are more irregular in form, size and distribution. Uneven growth above ground could be the result of many things e.g. lack of water unequal fertilizer application, soil structure.
#2. Potatoes in Syria often show reduced and weak growth but no obvious above-ground symptoms. The photo shows what is happening in the soil. What does this suggest as a likely cause?
The correct answer is:
Orobanche, parasitic plant. Note the distinct purple shoots coming from the potato tuber.
Comments:
Orobanche, or broomrape, is a genus with many species infecting a wide range of plants. It’s a widespread cause of significant losses in potatoes.
#3. Growth of Okra plants was uneven and sometimes stunted, as seen in South Africa. Below ground the root was swollen, as shown in the photo. The root has been cut lengthways to reveal internal symptoms. What is the cause?
#4. Above ground, this common bean plant shows poor growth. This is what I found when I examined the roots. Look closely at the photo for the likely cause.
The correct answer is:
Bean-root aphid (Trifidaphus phaseoli)
Comments on the other options:
Look closely and you can see the aphids feeding on the roots. At first I thought this was waterlogging, but digging up the plants clearly revealed the real cause.
#5. These are the cut fruit from a wilting banana plant in Uganda. Wilting was seen in young, emerging leaves, which gradually went from pale green to brown. What is the cause?
The correct answer is:
Xanthomonas bacterial wilt of banana
Comments on the other options:
Fusarium wilt affects older leaves and does not, usually, affect fruits. Xanthomonas wilt produces this distinctive staining in fruits and premature ripening (as does Ralstonia bacterial wilt – Moko disease). Fusarium wilted leaves are older and often go a bright yellow.
#6. The bark has been removed from this cacao tree in DRC. Above ground some branches are dying and leaves are dropping. What is the cause of the decline?
The correct answer is:
Armillaria root rot.
Comments on the other options:
It looks like a boring insect, yet the extensive white mycelium gives the game away. Armillaria is truly impressive in the number of species it can affect. It’s not a serious disease in eastern DRC, but one to look out for when diagnosing Verticillium wilt, a more common and serious problem.
#7. Above ground, leaves are wilting on this broad bean plant in Bolivia. The cut lower stem and root is shown in the photo. What is the cause?.
#8. The potato plant above ground had collapsed. The photo shows the appearance of the stem just above ground and the root below. What is the cause?
The correct answer is:
Fungal rot (Athelia rolfsii)
Comments:
Previously known as Sclerotium rolfsii, this is a widespread pathogen affecting many hosts. Note the distinctive sclerotia – the small white spheres – at the bottom of the photo. The abundant mycelium is also distinctive for this pathogen.
#9. Seen in routine testing of seed potatoes (those sold for next season’s planting).
#10. Damage seen inside the base (corm) of a banana, and linked to above ground collapse of plant and general decline. What is happening?
The correct answer is:
Banana weevil (Cosmopolites sordidus)
Comments:
There are many reasons why bananas decline, and the only way to identify the most likely cause is by looking inside the pseudostem and low down for tell-tale signs.- in this case the black pockets associated with weevil damage. Look closely and you can see the larva top left. Also known as the banana borer.
Results
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
